I imagine they might care because advertisements are their source of revenue on that platform, which I believe loses money regardless. They’re also getting increasingly adamant about breaking people’s ad blockers.

It also appears to me that every combination of functional use requires some form of identification:

• If you’re logged out, they’re okay with you browsing from an identifiable home IP address.
• If you’re on a VPN, they’re okay with showing your videos if you log in so they can track your viewing habits.
• If you’re on a VPN and make a new account, they want your phone number so they can tie your identity to an actual human being.

It might be a bit paranoid, but these factors combined suggest that Google does not want us to watch videos without providing some form of (inferrable) personal identification. And if Google can’t get what it wants, specifically data and ad revenue, they might be very willing to terminate an account that’s draining their coffers.